Flotation of iron ores



E. C. HERKENHOFF FLOTATION OF-IRON CRES Filed Dec. l0, 1942 ATTOR N EYPatented Nov. 27, 1945 FIDTATION F IRON GRES Earl Conrad Herkenhoil',Stamford, Conn., assignor to American Cyanamid Co N. Y., a corporationof Maine mpany, New York,

Application December 10, 1942, Serial No. 468.524

(cil 209-166) 6 Claims.

This invention relates to the beneiiciation of iron ores by frothflotation. More particularly, the invention relates to a multi-stagedotation lprocess suitable for use on :lines such as are found in theoverflow from iron ore washer plants; in waste products from heavy mediaseparation processes, and on those ores which mustl be nely ground 1norder to unlock the iron minerals from the gangue.

Increasing amount of the lower grade iron ores, such as those with whichthe present invention is concerned, are coming into industrialimportance because of the constantly decreasing amounts of availablehigh grade ore. Most of these ores are. too low in iron and too high insilica-bearing gangue to be suitable for use in blast furnaces.Consequently, if they are to be used they must be beneiiciated in somemanner. Frequently, calciumcarb'onate and other alkaline earth carbonateminerals are also found in the ores. These, of themselves, are notparticularly objectionable, in fact being to a certain extent desirable.In some cases, however, it may be necessary to remove a portion oftheseconstituents in order to raise the iron content.

The principal problem, therefore, is one of reducing the impurities andraising the iron content to as high a degree as possible. As was pointedout, this usually involves the removal of silica. The necessary degreeof beneciation can be accomplished in any one of several ways, dependingon the ore. In some cases, the necessary rise in iron content may bemade by merely crushing and washing the ore. Where the iron minerals andthe gangue are associated in such manner that this can not be done, butthe mineral values can be released with moderately ne crushing,heavy-media separation is particularly useful.

Much of the naturally occurring ore, however. requires line grinding inorder to enable separation of the objectionable gangue. After thenecessary grinding is done, beneiiciation by froth flotation is perhapsthe most useful method of separating the gangue from the mineral values.In addition to the ores of this type, there are the wastes from thewashing and the heavy-media processes mentioned above. Although too lowin iron content for ordinary use, because of the tremendous volumesinvolved they represent a very large amount of potentially useful ironmineral.

As pointed out above, one of the principal objectionable constituents isusually a silica-bearing mineral of some type or other. From the pointof view of susceptibility to froth notation, this is particularlyunfortunate since the iron minerals and these silica-bearing gangues aregenerally diilcult to separate. Because of this separational difficulty,a flotation process to be successfully carried out requires carefulhandling, usually also accompanied by a high reagent consumption. All ofthese factors tend to increase the cost of processing. Yet iron ores,despite the fact that they must be handled in enormous quantities, areintrinsically cheap products and the margin of profit is small.Therefore beneficiation by froth flotation, if it is to be carried out,must be done cheaply, easily and eiiiciently. In this respect, ordinarymethods of beneficiating ores by froth flotation when applied tu ironores leave much to be desired.

Ordinarily, separation of mineral values from silica-bearing gangues byfroth flotation takes one oi' two forms. Either the mineral is oatedfrom the silica by the use of an anionic-type reagent or reagentcombination, or the silica is oated from the mineral values by means ofa cationic-type of reagent. In general, anionic flotation is the easiestand cheapest and is, thereg5 fore, used whenever possible. 'I'he usualprocedures are old and well known in conjunction with many ores.

Unfortunately, when applied to ordinary iron ores of the type with whichthe present invention is concerned, anionic flotation does not workwell. The iron minerals and the gangue tend to oat together. By usingsufficient care and the necessary amount of reagents a beneficiation canbe carried out whereby some 30 to 40% of the iron values can berecovered, but the grade is usually too low. The grade can be improvedsomewhat at the expense of the recovery, but the net cost is much higherthan is practically desirable for the amount of mineral recovered at thecorresponding concentrations.

In like cases with other ores, the reverse procedure is useful, i. e.,silica is floated from the useful minerals with a cationic promoter.This process, when it can be properly used, is excellent. However, itsuffers from several inherent drawbacks which must be capable of beingovercome before the procedure can be said to be properly used. First ofall, cationic reagents are expensive, the unit cost being several timesthat oi equal amounts of anionic-type reagents. They depend forcompetitive success on the fact that if they can be used eiectively,they are highly selective and have great collecting power and so can beused in smaller amounts.

However, they must be very eiiiciently used and this involves a seconddii'liculty, that oi' slimes. Cationic reagents are particularlysensitive to the presence of slimes. even a fraction of a percent in thepulp often being suilicient to impair the efliciency of the reagent to apoint where the -reagent cost becomes prohibitive. A balance must bemade between the cost of preparing the ore such as the grinding,desliming, etc., the reagent cost, andthe amount of mineral recovered.Unfortunately, with most low grade iron ores this balance works outunfavorably. The cost of the preparation required plus the reagent costraises the total above that which can be expended for the amount of orerecovered if the latter is to be sold in a competitive market.

In general, the recovery of iron from low grade materials tends to belower than recoveries of non-ferrous metals from their ores. However, aspreviously stated, recovery is governed by economic factors which mayoutweigh metallurgical efllciency.

'Ihere remains, therefore, a demand for a suitable beneflciation processwhereby the iron content of low grade ores, .particularly the wastesfrom washer plants and the like, can be carried out at a cost which willpermit the process to be used on a large scale. It is the object of thepresent invention to establish a procedure of froth flotation by the useof which the desirable results of cheaper and more eiectiveconcentration of the iron minerals may be obtained with these low gradestarting materials.

In general, the desired object of the present invention is accomplishedby a multi-stage flotation. Inv the iirst stage, a major portion of theiron minerals and a part of the silica gangue is floated away from theremainder of the ore by means of an anionic-type promoter. Thisconcentrate is then subjected to a second anionic flotation in thepresence of an iron depressant. The tailings from this step are nallysubjected to a silica notation with a cationic reagent.

This procedure has a number of advantages. It uses the cheapest reagentson the biggest bulk of material whereby the latter is very appreciablyreduced before the more expensive reagents need be employed. In this waythe better features of both types of reagent are utilized to fullestadvantage. A greater proportion of the iron'minerals can be recovered ina higher grade product than was practically possible with any previouslyused procedure. On the base of the recovered iron product, the totalhandling and reagent costs are less than that for any of the previouslyknown and used beneciation methods. 'Ihe process, therefore, is not onlyhighly eilicient as compared with older methods, but is alsocommercially desirable since it can be readily used on a large scale.

The process of the present invention will be more fully discussed inconjunction with the accompanying drawing in which:

Figure 1 represents a flow scheme of the simplest arrangement involvingthe essential features of the present invention; and

Figure 2 represents a similar flow scheme' showing alternative flowswhich may be desirable with certain ores to improve with the grade orthe recovery.

The ore, as it is introduced into the process of the present invention,may as shown in Figure 2, be deslimed if necessary. The desliming step,however, as shown in Figure 1 is optional and the ore may ordinarily bepassed directly to a conditioning operation in which the pulp isconditioned with the anionic-type promoter and a frother, if the latteris to be used. The conditioned pulp is then subjected to flotation,whereby a concentrate rich in iron but containing a part of the gangue,is obtained. The taiiing, although having a rather high iron assay,usually represents such a small percent of the total iron in the feedthat it ordinarily may be discarded without further treatment.

The rougher concentrate may be cleaned, as shown in Figure 2 if sodesired, the tailing from which may be either discarded or recycled tothe original conditioning step. The rougher and cleaner concentrates arecombined and then conditioned with hydrated lime, quicklime or someequivalent alkaline earth oxide or hydroxide. This treatment serves theseveral purposes of overcoming the effects of any residual fatty acidfrom the anionic flotation, providing a depressant for the iron mineralsand acting in a manner which promotes the silica.

The conditioned pulp is then subjected to the primary silica flotationin which a concentrate high in silica and low in ironis obtained. Thisprimary silica concentrate may be directly discarded or it may besubjected to a cleaning operation, the concentrate from which isdiscarded.

This cleaning of the primary silica concentrate is not essential to theoperation of the process and may be omitted if the iron values in therougher concentrate are not high enough to warrant carrying out thisstep.

The tailings from the primary silica flotation and/or the primary silicacleaner operation are passed to a classier, and are washed and deslimed.The slimes are ordinarily discardedbut if it is so desired they may berecycled to the conditioning step just prior to the primary silicaflotation. The deslimed sands represent only a small proportion of thetotal volume of ore fed to the overall process but contain a largeproportion of the total iron content.

These sands are then subjected to a secondary silica flotation in thepresence of a cationic-type promoter. The tailing from this secondarysilica flotation represents the iron concentrate and may be solddirectly as ilnished iron product. The silica concentrate from thissecondary silica flotation step maybe directlydiscarded or may be givenan optional cleaning in which the concentrate is discarded and thetailing is recycled to join the fresh feed in the alkaline-earth metaloxide conditioning step.

It is an advantage of the present invention that despite its being amulti-stage flotation operation the process is in fact quite flexible sothat it can be adjusted for different ores. This may be noted, forexample, in the optional desliming and cleaning steps. In this regard,the cleaning is preferably done by notation, but it is also possible touse gravity methods of concentration such as tabling or vanning whensuch methods are advantageous.

Similarly the reagents used may be varied considerably without departingfrom the scope of the present invention. For example, in the anionicnotation. substantially any anionic-type promoter may be used. Excellentresults can be obtained using a fatty acid promoter such as oleic acid.However, the invention is not so limited and other promoters may besubstituted therefor such as fish oil fatty acids, coconut oil fattyacid, linseed oil fatty acids, cottonseed oil fatty acids, talloel andthe like, as well as their sodium, potassium and ammonium soaps andemulsions thereof. In most cases it ls desirable to use a. frother inconjunction with the amonio reagents. Any of the Well known frothers maybe used. Among these are pine oil, synthetic pine oil, cresylic acidsand certain aliphatic alcohol irothers. These may be used alone or inadmixture with each other or with other froth modifying agents.

As was pointed out above, the concentrate from the anionic notation isconditioned with an alkaline earth oxide or hydroxide such as hydratedlime. This apparently serves a double purpose although its action is notthoroughly understood. It does, however, appear to eliminate theundesirable results which are ordinarily obtained in the presence of anyexcess promoter from the anionic flotation when the latter is followedby cationic notation. In addition, a. distinct depressing action on theiron minerals is observed.

It has been found well to use a small amount of frother in carrying outthe primary silica flotation after thepulp has been conditioned with thealkaline earth hydroxide. Again, substantially any commerciallyavailable frother may be used. Ordinarily, however, only about one-halfas much frother is necessary as in the preceding anlonic notation stepand in many cases it may be eliminated entirely.

Similarly, the secondary silica flotation which is carried out in thepresence of a cationic promoter is not necessarily limited to the use ofany particular reagents. A choice as to the cationic promoter used maybe made from among the amines or amine salts such as lauryl aminehydrochloride and the like; quaternary onium compounds such as cetyltrimethyl ammonium bromide many of which are commercially available forthe purpose; or the polyalkylene-polyamine reaction products, many ofwhich are also commercially available for the purpose. Again, a, smallamount of frother such as pine oil or the like is desirable but notessential.

The invention will be described in greater detail in conjunction withthe following specic examples which are illustrative only and not meantto limit the scope of the present invention.

A sample of overflow Waste principally composed of hematite and quartzfrom an iron ore washed plant, which presented beneiiciation problemstypical of those which the present invention is concerned, was made intoa pulp containing about 20% solids, conditioned with 0.162 lb. per tonof a pine oil ircther and 0.75 lb. per ton of oleic acid and subjectedEXAMPLE 2 A sample of the same ore of Example 1 was then subjected totreatment according to the process of the present invention. Theundeslimed feed was conditioned at 23% solids for about 5 minutes in aFagergren flotation machine using 4 per ton of sodium silicate and 1.5lbs. per

ton of saponied tallcel. Pine oil, 0.081 lb. per ton, was added and thepulp was floated for 3 minutes. the tailing being discarded. 'I'heconcentrate was diluted to about 16% solids and conditioned for 4minutes with 4 lbs. per ton of hydrated lime and then floated for 5minutes with 0.054 lb. per ton of pine oil. The silica concentrate wasgiven a 4 minute cleaner notation with an additional 0.054 lb. per tonof pine oil and the cleaned concentrate discarded. The primary sillcaotation tail .and the silica cleaner tail were combined and deslimed byhydraulic classification. The overiiow containing the shimes wasdiscarded and the underilow iioated for 4 minutes in the presence of0.20 lb. per ton of 903-14, a cationic-type promoter marketed by theEmulsol Corporation, and 0.162 lb. per ton of pine oil. The silicaconcentrate was discarded and the tailing comprising the ironconcentrate set aside as product. The results are shown in Table I.

Table l' Percent dis- Percent Percent tribution weight Fe Feed 100.00Anionic tail 39. 74 Primary silica con 18. 77

1. Secondary silica conc.. 25. Iron conc 14.

EXAMPLE 3 The procedure of Example 1 was repeated on the same. ore withthe exception that the ore was deslimed by hydraulic classificationKbefore being subjected to the original conditioning step. From a headassaying 23.84% iron, a concentrate assaying 27.95% iron and containing37.70% of the total iron fed was obtained. The results although betterthan those of Example 1 are not even approximately the equivalent ofthose of Example 2.

EXAMPLE 4 The procedure of Example 2 was repeated on the same ore exceptthat the ore was deslimed before the initial conditioning step and theore was conditioned for only 2 minutes instead of 5. In the iinal silicaflotation 0.10 1b. per ton of an aliphatic amine hydrochloride(approximately Cis) was substituted for the 0.20 lb. per ton of CationicReagent 903L. The results are shown in Table II.

Table II Percent distrlbution Percent Percent weight Iron conc EXAMPLE 5A sample of ore containing hematite and quartz as the principalconstituents and assaying 19.73% iron was deslimed by hydraulicclassification using 1 lb. per ton of sodium silicate as a dispersant,the slimes being discarded. The sands were diluted to 21% solids andconditioned for 2 minutes with 0.75 lb. per ton of oleic acid and 0.162lb. per ton of pine oil. The conditioned pulp was oated for 5 minutesand the rougher tail discarded. concentrate was conditioned for '7minutes with 2 lbs. per ton of hydrated lime after which 0.054 lb. perton of pine oil was added and the pulp floated for 3 minutes. The silicaconcentrate was cleaned in a 5 minute flotation using 0.162 lb. per tonof pine oil and the Table III Percent distrlbution Percent Percentweight #l slimes Anlonic tail-H2 slimes.- Primery silica conc Secondarysilica conc Iron conc HHN New EXAMPLE 6 A sample of iron ore washertailings taken from the overflow in a bowl classifier and principallycomposed of hematite and quartz was dispersed with l lb. per ton ofsodium silicate and deslimed by hydraulic classification, the slimesbeing discarded. The sands were conditioned at 21% solids for 1 minutewith 0.50 lb. per ton of saponifled talloel after which an additional0.75 lb. per ton of saponified talloel and 0.135 lb. per ton of pine oilwere added and the pulp floated for 6 minutes, the tailings beingdiscarded. The concentrate was conditioned for 4 minutes at 19% solidswith 4.0 lbs. per ton of hydrated lime after which .054 1b. per ton ofpine oil was added and the pulp subjected to a 4 minute flotation. Thesilica concentrate was cleaned for 3 minutes with .0541b. per ton ofpine oil and the silica cleaner concentrate discarded. The rougher andcleaner tails were combined, deslimed and the underflow floated for 7minutes with 0.20 lb. per ton of "Lorol amine hydrochloride(approximately Ciz to C13) and 0.135 lb. per ton of pine oil. The silicaconcentrate was discarded and the tailings saved as the ironconcentrate. Results are shown in Table IV.

Table IV Percent Percent Fe distribution Anionic teil-H2 slime@Primarysilica conn Secondary silica mm` Iron armi'` 1L Exmu'l Theprocedure of Example 3 was repeated with several samples of the same oreused in Examples 5 and 6. Enough reagents were used to try to obtain thebest possible recovery. Iron concentrates assaying from 33 to 47% ironand representing about 43% of the total iron fed were obtained. As willbe seen from a comparison with Tables III and IV, these results do notcompare favorably with the grades of products obtained by the practiceof the present invention, despite the fact that more reagent wasrequired to obtain the maximum recovery.

I claim:

1. A method of beneciating low grade iron ores containing siliciousgangue by froth flotation which comprises the steps of making a pulp ofthe ore, subjecting the pulp to froth dotation in the presence of ananionic promoter selected from the group consisting of the higher fatty-acids, resin acids, talloel, and the sodium, potassium and ammoniumsoaps thereof, whereby a concentrate containing a major portion of theiron minerals and a part of the silica-bearing gangue is obtained,conditioning the concentrate with an alkaline-earth oxide in the absenceof cationic-type promoters, subjecting the conditioned pulp to a primarysilica notation in the absence of additional collecting agents, andsubjecting the talling from the primary silica flotation to a secondarysilica notation step in the presence of a cationic-type promoter.

2. A process according to claim 1 characterized in that the materialused as feed is deslimed before the initial flotation operation.

3. A method according to claim 1 characterized in that the primarysilicaA concentrate is subjected to a cleaner flotation, the cleanertailings being combined with the tailings from the primarysilicaflotation before being subjected to the cationic notation.

4. A process according to claim 1 characterized in that the initialflotation concentrate is cleaned, the cleaner concentrate beingconditioned with an alkaline earth oxide before the primary silicaflotation and the cleaner tailing being recycled to the feed.

5. A process according to claim 1 characterized in that the tailing fromthe primary silica notation is deslimed prior to the secondary flotationwith a cationic reagent.

6. A process according to claim 1 characterized in that the concentrateof the secondary silica flotation is subjected to a cleaning operation,the concentrate from which is discarded and the tailing is recycled tothe alkaline-earth oxide conditioning step.

EARL CONRAD I-IERKENHOFF.

